1. Field of the Invention
The present invention relates to a rechargeable battery and its fabrication method, and more particularly, the present invention relates to a rechargeable battery and its fabrication method, the battery preventing electrical shorts between the electrode plates by decreasing shrinkage of a separator of the battery.
2. Description of the Related Art
Various batteries have been used as a power source of small electronic devices. As a power source of portable phones, notebook computers, camcorders and the like, the battery using an electrolyte, such as a lithium rechargeable battery that is a small sealed battery of a large capacity has been generally used. As such an electrolyte battery, a cylindrical or a prismatic type battery has been used.
Generally, a rechargeable battery, such as a lithium rechargeable battery and a lithium polymer battery includes an electrode assembly with an electrolyte contained within the case. The electrode assembly includes a positive electrode plate, a separate and a negative electrode plate. The positive electrode plate (or negative electrode plate) includes a positive electrode (or negative electrode) collector in the type of foil and a positive electrode active material coated on the surface of the positive electrode collector. An uncoated region in which an active material has not been coated is formed on the collector of the plates, and an electrode tab is generally welded to the uncoated region for connection to an external circuit.
In more detail, the lithium rechargeable battery is formed by respectively coating an active material on the positive electrode collector and negative electrode collector and arranging it in a case as an electrode assembly of a wound jelly-roll type having a separator interposed between the collectors, and injecting an electrolyte and covering the opening of the case with a cap assembly.
The lithium rechargeable battery is classified into a cylindrical type battery having a jelly-roll arranged within a cylindrical case, and a prismatic type battery having the jelly-roll arranged within a prismatic case. However, the prismatic type rechargeable battery has been generally used for small or thin devices having a rectangular receptacle.
In the prismatic rechargeable battery, to arrange the electrode assembly in the case, the electrode assembly is wound, fixed by a finishing tape, and then pressed.
In other words, the finishing tape is attached by wrapping the end portion where the winding of the jelly-roll type electrode assembly has been finished at the circumferential surface of the jelly-roll type electrode assembly that is formed by winding a positive electrode plate, a separator and a negative electrode plate in sequence.
The positive electrode plate and negative electrode plate are formed generally by coating and filling an active material for a metal base, and drying, roll-pressing and cutting the metal base even though it is somewhat different depending on the kind of the rechargeable battery. For a lithium rechargeable battery, a lithium transition metal oxide is used as the active material of the positive electrode plate and aluminum is used as a collector of the positive electrode plate. Furthermore, carbon and carbon composite are used as the active material of the negative electrode plate and copper is used as a collector of the negative electrode plate.
Furthermore, the separator separates the positive electrode plate and the negative electrode plate so as to not directly contact to cause electrical shorts. A micro-porous film made of polyolefin resin, such as polyethylene or polypropylene, is used as the separator.
The separator is formed longer than the positive electrode plate and the negative electrode plate for preventing an electrical short caused by contact between the positive electrode plate and negative electrode plate when winding the positive electrode plate, the separator and the negative electrode plate.
However, an outmost base portion of the electrode assembly that the winding has been completed is fixed by a finishing tape after the positive electrode plate of aluminum (or the negative electrode plate of copper) has been finally wound and finished. In other words, the finishing tape is attached on the surface of the positive electrode collector of the positive electrode located at the outmost of the wound electrode assembly.
As described above, the finishing tape finishes the wound electrode assembly and simultaneously holds the positive electrode plate attached to the surface of the positive electrode collector of the positive electrode. However, because this finishing tape is not directly attached to the separator for preventing electrical shorts between the positive electrode plate and the negative electrode plate by being interposed between the positive electrode plate and the negative electrode plate, the finishing tape can not well hold the separator so as not to be deformed.
Accordingly, when the separator made of resin shrinks horizontally or longitudinally (vertically) due to a charge or discharge of the battery or a heat shock, especially when the separator shrinks horizontally or longitudinally (vertically) as a result of an electrode tab generating a large amount of heat at the upper region of the electrode assembly where much of the electrical current flows, because the separator shrinks and simultaneously the end portions of the positive electrode plate and the negative electrode plate contact each other, thereby causing an electrical short.